Many toxicants commonly found at Superfund sites are capable of inducing oxidative stress in animals and humans. The fact that many agencies induce oxidant stress suggests not only that these agents may act synergistically when mixtures of such chemicals are present, but also, that the ability of organisms to service and adapt to such mixed exposures may depend upon their ability to utilize cellular antioxidants and antioxidant enzymes to combat this stress. A very important enzyme involve din antioxidant defense is glutamate-cysteine ligase (GLCL), the rate limiting enzyme for the synthesis of the cellular antioxidant glutathione (GSH). The primary goal of this project will be to investigate the genetic and biochemical bases of GLCL regulation in mice and humans. We propose to ascertain the factors that control GLCL expression and activity, to develop murine models of GLCL over- expression of GLCL insufficiency, and to assess the frequency of the genetic polymorphisms in GLCL genes in humans affected with diseases or conditions associated with oxidative stress. Such information will be useful in determining the functional significance of this enzyme in defense against toxicants, and its utility as a biomarker of exposure and/or susceptibility to toxicants commonly found at hazardous waste sites that may act individually or synergistically to induce oxidant stress. Ultimately this information will be useful in minimizing uncertainties in risk evaluation for people and animals exposed to low doses of contaminants at Superfund sites.